Image pickup apparatus capable of performing image pickup with reduced flicker influence, method for controlling the same, and storage medium

ABSTRACT

There is provided with an image pickup apparatus including a detection unit configured to perform a flicker detection operation to detect flicker based on a plurality of images captured by an image sensor, and a control unit configured to control the image sensor based on detected flicker information. The detection unit configured to perform first detection of the flicker detection operation at a time that is different from a time at which an image pickup preparation instruction is received and different from a time at which an image pickup instruction is received whilst live view images are displayed. In the case that a flicker is detected in the first detection, the control unit configured to control exposure of the image sensor in a charge accumulation period to reduce an influence of the flicker for live view display on display means after the first detection.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.16/452,202, filed Jun. 25, 2019, which claims priority from JapanesePatent Applications No. 2018-125529, filed Jun. 29, 2018, No.2018-125530, filed Jun. 29, 2018, No. 2018-125531, filed Jun. 29, 2018,No. 2018-125533, filed Jun. 29, 2018, No. 2018-125532, filed Jun. 29,2018, and No. 2019-093204, filed May 16, 2019, which are herebyincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image pickup apparatus such as adigital camera, and more particularly to a technique for reducing aninfluence resulting from a periodical light amount change (generallyreferred to as a flicker) by an artificial light source when capturingan image of a subject.

Description of the Related Art

It has conventionally been known that, an artificial light source suchas a fluorescent light is affected by a commercial power frequency, andthe light amount periodically changes to fluctuate illumination light,i.e., a flicker occurs. Under a flicker light source producing such aflicker, if an image of a subject is captured at a shutter speed (orcharge accumulation period) shorter than the light amount change periodof the flicker, unevenness in brightness and color may occur in oneimage and among a plurality of images captured in continuous imagecapturing.

A flicker affects not only a still image but also a moving image. Whensuccessively displaying images captured by using an image sensor under aflicker light source on a display unit, what is called displaying a liveview, stripes arise in the image or the brightness of the entire imagechanges because of a flicker according to the charge accumulation periodand frame rate of the image sensor.

Japanese Patent Application Laid-Open No. 2009-213076 discusses atechnique for detecting a flicker according to changes of a lightsource, and setting the charge accumulation period of an image sensor asan integral multiple of the light amount change period of the flicker,thus solving the influence of the flicker.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, an image pickupapparatus includes an image sensor, a display unit configured to displaya live view for successively displaying images captured by using theimage sensor, a detection unit configured to perform a flicker detectionoperation to detect flicker based on a plurality of images captured bythe image sensor at predetermined intervals, a control unit configuredto control the image sensor based on flicker information detected by thedetection unit, and an operation unit configured to enable a user toperform a manual operation to instruct the detection unit to start theflicker detection operation. The detection unit performs first detectionof the flicker detection operation in response to an image pickupinstruction by the user. The detection unit performs second detection ofthe flicker detection operation upon an operation on the operation unitby the user at a time that is different from a time at which the imagepickup instruction is received while live view images are displayed onthe display unit. When a flicker is detected in the first detection, thecontrol unit controls exposure of the image sensor to perform imagepickup in accordance with a predetermined timing of a light amountchange in the detected flicker.

Further features of the present invention will become apparent from thefollowing description of embodiments with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an overview of an image pickupsystem according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating details of the image pickupsystem according to the first embodiment of the present invention.

FIG. 3 is a flowchart illustrating image capturing processing forperforming flicker detection during live view display according to thefirst embodiment of the present invention.

FIGS. 4A and 4B illustrate a charge accumulation timing and a chargereadout timing related to an image signal for flicker detectionaccording to the first embodiment of the present invention.

FIGS. 5A, 5B, and 5C illustrate methods for determining a light amountchange period of a flicker according to the first embodiment of thepresent invention.

FIG. 6 illustrates a method for calculating a flicker peak timingaccording to an embodiment of the present invention.

FIG. 7 illustrates a timing chart related to a flickerless imagecapturing operation during live view display according to the firstembodiment of the present invention.

FIG. 8 is a flowchart illustrating processing related to a flickerdetection operation during live view display according to the firstembodiment of the present invention.

FIG. 9 is a flowchart illustrating image capturing processing duringlive view display according to the first embodiment of the presentinvention.

FIG. 10 is a flowchart illustrating flickerless image capturingprocessing in a case where a flickerless image capturing function isturned on, according to a second embodiment of the present invention.

FIG. 11 illustrates a method for calculating, when a flicker exists, aphotometry value (luminance value) in accordance with the light amountchange period of the flicker.

FIG. 12 illustrates a relation between a light amount change period andan exposure time of a flicker.

FIG. 13 illustrates a method for calculating an exposure correctionamount according to the second embodiment of the present invention.

FIG. 14 is a flowchart illustrating image capturing processing forperforming flicker detection during live view display according to athird embodiment of the present invention.

FIGS. 15A and 15B illustrate timing charts and aperture states relatedto flickerless image capturing processing for each of lenses withdifferent aperture driving methods according to the third embodiment ofthe present invention.

FIGS. 16A and 16B illustrate timing charts and aperture states relatedto a case of driving an aperture in a flicker detection operation foreach of lenses with different aperture driving methods according to thethird embodiment of the present invention.

FIG. 17 is a flowchart illustrating flicker detection processing inlight emission image capturing according to a fourth embodiment of thepresent invention.

FIGS. 18A, 18B, and 18C are timing charts illustrating flicker detectionprocessing in light emission image capturing according to the fourthembodiment of the present invention.

FIG. 19 is a flowchart illustrating flicker detection processing inlight emission image capturing in consideration of a difference in theshutter driving method and a result of moving object detection accordingto the fourth embodiment of the present invention.

FIG. 20 is a flowchart illustrating flickerless image capturingprocessing in a case where the flickerless image capturing function isturned on, according to a first modification of the present invention.

FIG. 21 is a flowchart illustrating flickerless image capturingprocessing in a case where the flickerless image capturing function isturned on, according to a second modification of the present invention.

FIG. 22 is a flowchart illustrating flickerless image capturingprocessing in a case where the flickerless image capturing function isturned on, according to a third modification of the present invention.

DESCRIPTION OF THE EMBODIMENTS

embodiments of the present invention will be described below withreference to the accompanying drawings. Each of the embodiments of thepresent invention described below can be implemented solely or as acombination of a plurality of the embodiments. Also, features fromdifferent embodiments can be combined where necessary or where thecombination of elements or features from individual embodiments in asingle embodiment is beneficial.

An image pickup apparatus according to a first embodiment of the presentinvention will be described below with reference to FIGS. 1 to 6. FIG. 1is a block diagram illustrating an overview of an image pickup systemaccording to the first embodiment of the present invention. FIG. 2 is ablock diagram illustrating details of the image pickup system accordingto the first embodiment of the present invention. The image pickupsystem including a camera main body 100, an imaging lens 200, and anexternal stroboscope 300 as the image pickup apparatus according to thefirst embodiment of the present invention will be described below withreference to FIGS. 1 and 2.

One or more function blocks illustrated in FIGS. 1 and 2 may beimplemented by hardware such as an application specific integratedcircuit (ASIC) or a programmable logic array (PLA), or implemented whena programmable processor such as a central processing unit (CPU) or amicroprocessing unit (MPU) executes software. In addition, the functionblocks may be implemented by a combination of software and hardware.Therefore, in the following descriptions, even if different functionblocks are described as operating entities, these function blocks areimplementable by the same hardware entity.

The camera main body 100 of a digital camera is an image pickupapparatus according to the present embodiment. An image sensor 101 is acharge accumulation type solid-state image sensor, such as a chargecoupled device (CCD) sensor or a complementary metal oxide semiconductor(CMOS) sensor including an infrared cut filter and a low-pass filter.The image sensor 101 forms an optical image corresponding to the lightflux of a subject guided by the imaging lens 200. Images picked up byusing the image sensor 101 are successively displayed at a display unit103 (described below) to achieve what is called a live view function.Images picked up by the image sensor 101 are also used as capturedimages for flicker detection and recording (described below).

A shutter 102 is a light shielding member disposed on the anterior sideof the image sensor 101 on the optical path of the light flux guided bya lens group 201. The shutter 102 includes a blade member. In a statewhere the blade member is opened, the light flux from the subject can beintercepted. In a state where the blade member is folded, an opticalimage corresponding to the light flux from the subject focused on theimage sensor 101 can be formed on the image sensor 101. The camera mainbody 100 is capable of adjusting the amount of light incident to theimage sensor 101 according to the running speed of the shutter 102. Thebrightness of the image signal can be adjusted by changing the shutterspeed as an exposure condition based on the running speed of the shutter102 and the exposure time of the image sensor 101. As a configurationfor performing a similar operation to the shutter 102, an electronicshutter operating through accumulation control in the image sensor 101may be adopted.

A display unit (hereinafter simply referred to as a display) 103 is athin-film transistor drive type liquid crystal display unit (TFT typeLCD). The display 103 can display an image for display based oninformation about image capturing parameters, such as the exposure forsubject image capturing and an image captured by using the image sensor101, enabling a live view (display) for successively displaying theimage for display. The display 103 is what is called a touch panel whichalso serves as an operation unit enabling the user to perform touchoperations. According to the present embodiment, the display 103functions as a capacitance touch panel. The configuration of the displayunit 103 enabling touch operations is not limited to capacitancedetection. Any known methods are applicable to the display unit 103.

The system control unit (CPU) 104 totally controls the camera main body100 and each unit of a camera accessory attached to the camera main body100. The contents of control performed by the CPU 104 will be describedin detail below in the descriptions of various operations.

The imaging lens 200 is an optical apparatus for guiding the light fluxcorresponding to the optical image of the subject to the inside of thecamera main body 100. The lens group 201 of the imaging lens 200 is anoptical system including a focus lens, a zoom lens, and a shift lens. Anaperture 202 is a light amount adjustment member for adjusting theamount of light incident to the inside of the camera main body 100 byadjusting the diameter of the aperture opening.

The imaging lens 200 includes a lens positioning unit (LPU) 203 as acontrol unit for the imaging lens. The LPU 203 controls the lensposition of the lens group 201 and the aperture diameter of the aperture202 and also serves as a communication control unit for controllingcommunication with the CPU 104 of the camera main body 100.

An aperture drive unit 205 is a component for driving the aperture 202of the imaging lens 200. More specifically, the aperture drive unit 205drives the aperture 202 to the aperture position specified by the LPU203 to adjust the opening of the aperture 202 to the open area amountcorresponding to the aperture value. A lens drive unit 204 is acomponent for driving the lens group 201 of the imaging lens 200 to apredetermined position, i.e., the position specified by the LPU 203.

The shutter control unit 105 is a component for controlling theopening/closing state of the shutter 102. Controlling the running stateof the shutter 102 in the time period specified by CPU 104 enablescontrolling the shutter speed for subject image capturing. A signalprocessing unit 106 is a component for performing various types ofprocessing on the image signal output from the image sensor 101. Morespecifically, the signal processing unit 106 performs predeterminedimage interpolation, resizing processing such as reduction, colorconversion processing, and processing for calculating the amount ofpixel data including saturated pixels and underexposure pixels, ondigital image data. The signal processing unit 106 is a white balance(WB) processing unit for performing white balance (hereinafter simplyreferred to as WB) calculation processing on digital image data.

A recording unit 112 is a recording medium for recording the imagesignal acquired in image pickup. The recording unit 112 is capable ofrecording the image signal acquired by using the image sensor 101 asstill image data or video data. The recording unit 112 is used also as amemory for recording data related to operations of the image pickupsystem centering on the camera main body 100 and various data acquiredby using the camera main body 100. The recording unit 112 according tothe present embodiment includes a read only memory (ROM) area usable asa nonvolatile memory and a random access memory (RAM) area usable as avolatile memory.

An image capturing mode selection unit 109 selects one of imagecapturing modes settable on the camera main body 100. The imagecapturing modes according to the present embodiment are modes providingdifferent methods for setting exposure-related elements (exposurecontrol values). Examples of settable image capturing modes include anaperture-value (Av) priority mode for preferentially setting theaperture value, and a shutter-speed (Tv) priority mode forpreferentially setting the shutter speed. The image capturing modeselection unit 109 is electrically connected with the CPU 104 whichcontrols the camera main body 100 according to the image capturing modeselected via the image capturing mode selection unit 109.

An image pickup instruction unit 110 is electrically connected with theCPU 104. When the user manually presses the image pickup instructionunit 110, a signal is enabled to issue an image-pickup preparationinstruction and an image pickup instruction. In other states, the signalis disabled. The image pickup instruction unit 110 changes in two stepsof the depression state. The CPU 104 recognizes the half-press state ofthe image pickup instruction unit 110 as an image pickup standby state,and instructs each unit of the image pickup apparatus 100 to perform animage-pickup preparation operation. The CPU 104 recognizes thefull-press state of the image pickup instruction unit 110 as an imagepickup state, and instructs each unit of the image pickup system toperform an image pickup operation.

An image pickup setting input unit 111 is an information input unit usedto set various modes and functions in the camera main body 100.Although, in the present embodiment, the image pickup setting input unit111 includes a rotating dial, a four-way operation key, an apply button,and a reset button, a mechanism used for information input is notlimited thereto. Typical modes and functions settable by using the imagepickup setting input unit 111 include various settings related to thephotometry mode, image capturing mode, continuous image capturingfunction, flickerless image capturing function (described below), liveview, and light emission image capturing function. When the image pickupsetting input unit 111 is operated, graphical user interfaces (GUIs) andfunction icons related to these functions are displayed on the display103.

Photometry modes, as modes for evaluating the entire screencorresponding to the field angle of the image sensor 101, includeevaluation photometry for performing correction according to thefocusing point and luminance value, and center-weighted photometry forperforming photometry with the center portion of the screen more largelyweighted than other regions. Other photometry modes include spotphotometry for performing photometry based only on a part of the screen,and partial photometry for performing photometry based only on apredetermined region on the screen which is larger than a spot.

Live view display methods (modes) include a normal mode in which acomposition check is possible, in consideration of the appearance of thelive view, and a simulation mode in which the exposure when performingmain subject image capturing and capturing a still image for recording(recording image) is simulated in the live view. One of differencesbetween the normal and the simulation modes is whether the exposurecorrection amount manually input by the user is reflected to the liveview. In the normal mode, the exposure correction amount is notreflected to the live view. In the simulation mode, the exposurecorrection amount is reflected to the live view with the user'sintention given priority.

A subject luminance determination unit 107 is a luminance detection unitfor determining (detecting) the brightness (luminance value) of thesubject based on the image signal output from the signal processing unit106. More specifically, the subject luminance determination unit 107divides one screen corresponding to the acquired image signal into aplurality of blocks and calculates the average luminance value for eachblock. Then, the subject luminance determination unit 107 integrates theaverage luminance value of each block to acquire the representativeluminance value. In the subsequent descriptions, the representativeluminance value is regarded as the luminance value (photometry value) ofthe subject, and the luminance value is used for various types ofprocessing and control such as the exposure control. The method fordetecting the luminance value is not limited thereto, and various typesof methods for the luminance value calculation are applicable. The CPU104 calculates the exposure control amounts of various exposure controlvalues (shutter speed, aperture value, ISO sensitivity, etc.) based onthe luminance value detected by the subject luminance determination unit107 and the image capturing mode selected by the image capturing modeselection unit 109.

A focal length determination unit 108 calculates information fordetermining whether the lens position of the focus lens included in theimaging lens 200 is in the in-focus state, based on the image signaloutput from the signal processing unit 106. If the current lens positionis determined to be in the out-of-focus state based on the calculatedinformation, the CPU 104 controls the imaging lens 200 via the LPU 203.Regardless of the in-focus state, the position of the focus lens can beadjusted under the control of the CPU 104 in response to an input of auser operation.

When the CPU 104 determines that the illumination on the subject isrequired through light emission determination based on the luminancevalue, a stroboscope control unit 113 performs light emission control ona light emission unit in response to a user manual operation. The lightemission unit according to the present embodiment is a built-instroboscope 114 built in the camera main body 100 or the externalstroboscope 300 detachably attached to the camera main body 100 via aconnection unit (not illustrated).

The external stroboscope 300, an external light emitting devicedetachably attached to the camera main body 100, includes an externalstroboscope control unit (SPU) 301 for controlling the operation of theexternal stroboscope 300. The SPU 301 is a control unit for controllinglight emitting of the external stroboscope 300 and communication withthe camera main body 100.

(Flicker Detection and Flickerless Image Capturing Functions)

The flicker detection operation during live view display on the cameramain body 100 will be described below with reference to FIG. 3. FIG. 3is a flowchart illustrating image capturing processing for performingthe flicker detection during live view display according to the firstembodiment of the present invention. The following descriptions will bemade centering on a case where live view display is started when thepower switch (not illustrated) of the camera main body 100 is turned onwith the flickerless image capturing function turned on in advance.

When the power switch of the camera main body 100 is turned on, then instep S101, the CPU 104 captures an image by using the image sensor 101and performs a photometry operation based on the image. The photometryoperation (first photometry) is performed to achieve suitable exposureconditions when performing subject image pickup (exposure time, aperturevalue, and ISO sensitivity) before starting an operation for the liveview or flicker detection.

In step S102, the CPU 104 performs the flicker detection operation. Theflicker detection operation according to the present embodiment will bedescribed below with reference to FIGS. 4A and 4B. FIGS. 4A and 4Billustrate a charge accumulation timing and a charge readout timingrelated to the image signal for flicker detection according to the firstembodiment of the present invention. The CPU 104 continuously performsthe accumulation and readout operations 12 times at a frame rate of 600frames per second (fps) and at intervals of about 1,667 milliseconds.

The value 600 fps equals the least common multiple of the light amountchange intervals (100 Hz and 120 Hz) of a flicker to be estimated inadvance. Performing the accumulation operation 12 times at 600 fps meansperforming the accumulation operations during a time period of 20milliseconds on an overall operation basis. Whichever commercial powerfrequency, 50 or 60 Hz, is used, two light amount change periods of aflicker light source will be included. All of the 12 accumulationoperations are performed under the same exposure conditions which aredetermined based on the result of the photometry operation in step S101.Not all the pixels of the image sensor 101 may be used for theaccumulation and readout operations at 600 fps. The frame rate may beadjusted to 600 fps (1,667-ms intervals) by performing what is calledpixel addition readout and thinning readout. As the luminance value tobe used as a reference when determining the exposure at the time of600-fps drive, values output from regions of the image sensor 101 usedfor the flicker detection operation are desirably used.

FIG. 4A illustrates accumulation control and an image signal outputtransition when a flicker occurs by the 50-Hz commercial power (atflicker turn-on intervals of 100 Hz). As illustrated in FIG. 4A, then-th accumulation is referred to as “ACCUMULATION n”, the n-th readoutis referred to as “READOUT n”, and the output of the image signal(photometry value) which can be acquired based on the result of READOUTn is referred to as “AE(n)”. According to the present embodiment, theCPU 104 performs the accumulation operation 12 times in a series offlicker detection operations to acquire outputs AE(1) to AE(12). Theacquisition time of each output is represented by the median in thecharge accumulation period since the CPU 104 performs the accumulationoperation in a limited time period.

The evaluation value to be used for the determination of the lightamount change period (frequency) of a flicker is calculated based onthese outputs AE(1) to AE(12). According to the present embodiment, theevaluation value to be used to determine the light amount change periodof the flicker will be defined by the following Formula (1).

$\begin{matrix}{{{SAD}(m)} = {\sum\limits_{i = 1}^{6}{{{{AE}(n)} - {{AE}\left( {n + m} \right)}}}}} & (1)\end{matrix}$

Sum of Absolute Difference (SAD) is used as an index representing thesimilarity in the field of pattern matching. A numerical value m meansthe calculation of the similarity between the output of the n-th outputAE(n) and the output of the (n+m)-th output AE(n+m) out of 12accumulation operations. SAD(m) calculates the similarity between theoutput of the n-th output AE(n) and the output after a time lapse of(1.667×m) milliseconds. As represented by the Formula (1), the value ofSAD(m) decreases with increasing similarity.

For example, under a 100-Hz flicker light source, the light amountchange period of the flicker is about 10 milliseconds, and the relationwith a flicker detection interval of 1.667 milliseconds is 10/1.667≈6.Therefore, as illustrated in FIG. 4A, the same output is acquired atintervals of six operations regardless of charge accumulation timing,resulting in a relation AE(n)≈AE(n+6). Based on this characteristics,SAD(6) is calculated to SAD(6)≈0 under a 100-Hz flicker light source.SAD(3) is additionally calculated to detect the presence of a 100-Hzflicker. SAD(3) is the calculated value of the similarity with theoutput after a time lapse of 1.667×3=5 milliseconds. Under a 100-Hzflicker light source, since the photometry values at 5-ms differenttiming are in a reversed phase relation, SAD(3) has a very large valuecompared to SAD(6). More specifically, in a case of large SAD(3) andsmall SAD(6), it is thought that a flicker corresponding to the 100-Hzlight amount change period may occur (exist).

FIG. 4B illustrates accumulation control and an image signal outputtransition when a flicker occurs by the 60-Hz commercial power (atflicker turn-on intervals of 120 Hz). Like the case where the lightamount change period of the flicker is 100 Hz, SAD(5) and SAD(3) arecalculated when a flicker occurs by the 60-Hz commercial power (atflicker turn-on intervals of 120 Hz). Under a 120-Hz flicker lightsource, since the light amount change period of the flicker is about8.333 milliseconds, AE(n)≈AE(n+5) and therefore SAD(5)≈0. Under a 120-Hzflicker, photometry values are in a reversed phase relation after a timelapse of 4.16 milliseconds. In this case, it is ideal to determine thesimilarity with the waveform after a time lapse of 4.16 milliseconds.However, since 4.16 milliseconds is not an integral multiple of a frameperiod of 1.667 milliseconds, the value of SAD(3) indicating thesimilarity with the waveform after a time lapse of 5 milliseconds as acomparatively close value is alternatively used. More specifically, alsounder a 120-Hz flicker light source, since SAD(3) indicates thesimilarity of photometry value change at an interval close to thereversed phase, SAD(3) has a very large value compared to SAD(5).

As described above, the CPU 104 calculates SAD(6), SAD(5), and SAD(3) tofinally determine the light amount change period of the flicker by usingthese evaluation values. FIGS. 5A, 5B, and 5C illustrate methods fordetermining the light amount change period of the flicker according tothe first embodiment of the present invention. FIG. 5A illustrates dataused to determine a flicker having a light amount change period of 100Hz. FIG. 5B illustrates data used to determine a flicker with a lightamount change period of 120 Hz. FIG. 5C illustrates data used to detectthe presence or absence of a flicker and the light amount change period.

As described above, under a 100-Hz flicker light source, SAD(3) has avery large value compared to SAD(6). Therefore, considering a plane withthe horizontal axis assigned SAD(3) and the vertical axis assignedSAD(6), as illustrated in FIG. 5A, plots are acquired in the relativelylower right region on this plane under a 100-Hz flicker light source.More specifically, in the region segmentation illustrated in FIG. 5A, aregion determined to be a 100-Hz flicker and a region determined to benon-100-Hz flicker are set. A 100-Hz flicker can be accuratelydetermined based on the plot position in these regions.

Likewise, in the region segmentation for a plane with the horizontalaxis assigned SAD(3) and the vertical axis assigned SAD(5), asillustrated in FIG. 5B, a 120-Hz flicker can also be determined. Theregion segmentation lines illustrated in FIGS. 5A and 5B are to beconsidered as examples. The inclination and inflection points of eachdivision line are not limited thereto.

The CPU 104 performs the final flicker detection by integrating theresults of determinations on the presence or absence of a flickerrelated to the above-described light amount change periods. According tothe present embodiment, the CPU 104 performs the final flicker detectionrelated to the detection of the presence or absence of a flicker and thelight amount change period by using the correspondence table illustratedin FIG. 5C. When no flicker exists (“DC” in FIG. 5C), the outputsthrough the 12 accumulation operations do not largely change in time.Therefore, a comparison of the outputs gives AE(1)≈AE(2)≈AE(3)≈ . . .≈AE(12), resulting in the evaluation values SAD(6)≈SAD(5)≈SAD(3)≈0. Inthis case, since plots are acquired near the origin on the planesillustrated in FIGS. 5A and 5B, the CPU 104 determines that neither a100-Hz flicker nor a 120-Hz flicker exists (occurs). Therefore, “DC” inthe lower right box in the table illustrated in FIG. 5C is applied.

The box at the upper left of the table illustrated in FIG. 5C indicatesthe occurrence of a 100-Hz flicker and a 120-Hz flicker. Such adetermination result is not normally acquired. However, for example, ifthe subject changes during 12 accumulation operations because of themovement of the subject or a panning operation, the result is notlimited thereto. In this case, since the result of the flicker detectionis an error, the CPU 104 determines that no flicker exists (detected).This completes the description of the flicker detection operation instep S102.

Returning to FIG. 3, when the CPU 104 detects a 100-Hz flicker (100 Hzin step S102), the processing proceeds to step S103. In step S103, theCPU 104 displays a message “FLICKER DETECTED” on the display 103 tonotify the user that a flicker has been detected. This display fornotifying the user that a flicker has been detected may be superimposedon the live view image, or displayed with the live view temporarilystopped.

The method for notifying the user of the flicker detection is notlimited thereto. A notification in any form and any format is applicableas long as the flicker detection can be notified to the user. Forexample, a function icon indicating the flicker detection may bedisplayed on a GUI on the display 103, or the flicker detection may benotified with sound by using a speaker (not illustrated) in addition tothe display on the display 103. Not only the flicker detection but alsothe light amount change period of the detected flicker may be notifiedat the same time.

In step S104, the CPU 104 sets the charge accumulation period of theimage sensor 101 as an integer multiple of the 100-Hz light amountchange period (10 milliseconds) of the flicker and performs a live view.The CPU 104 periodically performs the photometry operation on thesubject based on the image for live view even during live view displayand performs the exposure control based on the photometry result.

Factors which interrupt the live view include a flicker detectionoperation requested by the user, a power-off operation, and an operationfor subject image capturing. These elements will be described below inthis order.

In step S105, the CPU 104 determines whether the flicker detectionoperation has been performed by the user request. The CPU 104 performsthe flicker detection operation when the user touches the icon forflicker detection displayed on the display 103. When the CPU 104determines that the flicker detection operation has been performed bythe user request (YES in step S105), the processing returns to stepS102. Then, the CPU 104 repeats the flicker detection operation. In thiscase, the drive of the image sensor 101 is changed from the drive forlive view to the drive for flicker detection (600-fps drive). Theexposure conditions for the 600-fps drive are set from the photometryresult based on the last live view image.

As described above, an image to be used for the flicker detection issubjected to pixel addition or thinning readout. Therefore, when thedrive of the image sensor 101 is changed from the drive for live view tothe drive for flicker detection, an image with a low resolution may betemporarily displayed. Then, the CPU 104 does not display the imagecaptured with the 600-fps drive for flicker detection on the display 103(not used for the live view). Meanwhile, the CPU 104 continuouslydisplays the image for live view captured last on the display 103 (thisstate is referred to as a frame stop).

The CPU 104 needs to perform the 600-fps drive for flicker detectiononly in the 12 charge accumulation periods. If the time until thecompletion of the flicker detection operation is included, the drivecompletes in a short period for about 30 milliseconds. Therefore, evenif the CPU 104 performs the flicker detection operation by the user'sintention, the CPU 104 only needs to perform a frame stop for about 30milliseconds after the flicker detection operation. This enables theuser to easily know the result of the flicker detection operation whilepreventing the user from feeling strangeness as much as possible.

On the other hand, when the CPU 104 determines that the flickerdetection operation has been performed by the user request (NO in stepS105), the processing proceeds to step S106. In step S106, the CPU 104determines whether a power-off operation has been performed by the user.When the CPU 104 determines that the power-off operation has beenperformed by the user (YES in step S106), the processing proceeds tostep S122. In step S122, the CPU 104 cancels the live view and turns offpower of the camera main body 100.

On the other hand, when the CPU 104 determines that the power-offoperation has been not performed by the user (NO in step S106), theprocessing proceeds to step S107. In step S107, the CPU 104 determineswhether the image capturing operation has been performed by the user.When the CPU 104 determines that the image capturing operation has beenperformed by the user (YES in step S107), the CPU 104 cancels the liveview and the processing proceeds to step S118 and the subsequent steps.In step S118 and the subsequent steps, the CPU 104 performs the flickerdetection and flickerless image capturing. The flicker detection andflickerless image capturing based on the image capturing operation willbe described in detail below.

When the CPU 104 detects a 120-Hz flicker (120 Hz in step S102), theprocessing proceeds to step S108. Processing in steps S108 to S112 willbe described below. Processing when a 120-Hz flicker is detected isbasically identical to the processing when a 100-Hz flicker is detected.More specifically, the processing in steps S108 to S112 is almostidentical to the processing in steps S103 to S107. However, the chargeaccumulation period of the image sensor 101 when capturing an image forlive view in step S109 is set to an integer multiple of the 120-Hz lightamount change period (about 8.33 milliseconds) of the flicker to reducethe influence of the 120-Hz flicker.

When the CPU 104 detects no flicker (DC in step S102), the processingproceeds to step S113. Processing in steps S113 to S117 will bedescribed below. Processing when no flicker is detected is basically thesame as the processing when a 100 Hz or 120-Hz flicker is detected.However, since no flicker is detected in this case, then in step S113,the CPU 104 displays a message “FLICKER IS NOT DETECTED” on the display103. In step S114, the CPU 104 does not need to control the chargeaccumulation period of the image sensor 101 in accordance with the lightamount change period of the flicker, the CPU 104 performs the exposurecontrol to achieve the optimum charge accumulation period based on thephotometry result.

In the processing in steps S103 to S117, as described above, when theuser performs the flicker detection operation during live view display,the CPU 104 performs the flicker detection operation and informs theuser of the detection result. As the exposure control for capturing animage for live view, the CPU 104 controls the charge accumulation periodduring live view display according to the result of the flickerdetection, making it possible to effectively reduce the influence of theflicker in the live view.

In step S118, immediately before the main subject image capturing, theCPU 104 performs processing for performing the flicker detectionoperation and calculating the peak timing of the light amount change ofthe flicker. The following describes the reason why the CPU 104 performsthe flicker detection operation upon execution of the image capturingoperation by the user (upon issuance of the image pickup instruction).As described above, according to the present embodiment, the CPU 104performs the flicker detection operation immediately after power of thecamera main body 100 is turned on (i.e., immediately before live viewdisplay is started) when the user performs a flicker detection operation(issues a flicker detection instruction). However, in a configurationwhere the flicker detection operation is performed only at thesetimings, the CPU 104 may execute the flickerless image capturingfunction since the flicker detection cannot be suitably performed.

For example, if a lens cap is attached to the imaging lens 200 whenpower of the camera main body 100 is turned on, the CPU 104 cannotexactly perform the flicker detection before starting live view display.In this state, if an instruction for main subject image capturing(recording image acquisition operation) is issued without the flickerdetection operation by the user, the CPU 104 will perform imagecapturing under conditions similar to those in a case where no flickeroccurs, even under a flicker light source. Furthermore, for example,even if the user performs the flicker detection operation, when theimage capturing environment changes before and after the flickerdetection operation (for example, when the user moves between indoor andoutdoor environments), a difference may possibly occur between theflicker detection result and the actual image capturing environment. Inany one of the above-described cases, it is likely that the imagecaptured in main image capturing is affected by the flicker or that arelease time lag increases even not under a flicker light source.

According to the present embodiment, therefore, the CPU 104 performs theflicker detection operation immediately before main image capturing. Theflicker detection operation in step S118 is identical to that in stepS102 described above, and redundant descriptions thereof will beomitted. In step S118, the CPU 104 calculates a flicker peak timing inaccordance with the flicker detection operation. The calculation will bedescribed in detail below.

FIG. 6 illustrates a method for calculating a flicker peak timingaccording to an embodiment of the present invention. Among outputs forflicker detection AE(1) to AE(12), the point where the maximum output isacquired is represented by P2(t(m), AE(m)), the point of the precedingphotometry result is represented by P1(t(m−1), AE(m−1)), and the pointof the following photometry result is represented by P3(t(m+1),AE(m+1)). Referring to FIG. 6, the straight line passing through thepoint (the point P1 in this case) taking the smaller one of the outputAE(m−1) and AE(m+1), and the point P2 is acquired as L1=at+b. Thestraight line passing through the point (the point P3 in this case)taking the larger one of the output AE1 or AE3, having the inclination−a is acquired as L2.

By calculating the intersection of the lines L1 and L2, a flicker peaktiming t_peak can be approximately calculated. When the result of theflicker detection in step S118 is a 100-Hz flicker (100 Hz in stepS118), a flicker peak occurs at intervals of 10 milliseconds representedby t_peak+m*10 (in milliseconds, where m denotes an arbitrary naturalnumber).

Returning to FIG. 3, in step S119, the CPU 104 performs the mainexposure on the image sensor 101 at the first timing t_peak+m*10 reachedin a state where various image capturing preparations are completedafter execution of the image capturing operation by the user. Accordingto the present embodiment, to prevent unevenness in brightness in thevertical direction of an image captured through main image capturing,the CPU 104 controls the exposure period of the image sensor 101 basedon the flicker peak timing.

Likewise, when a 120-Hz flicker is detected in step S118 (120 Hz in stepS118), a flicker peak occurs at intervals of about 8.33 millisecondsrepresented by t_peak+m*8.33 (in milliseconds, where m denotes anarbitrary natural number). Therefore, in step S120, the CPU 104 performsthe main exposure in synchronization with the peak timing t_peak+m*8.33of the flicker by using a method similar to that in step S119. Theabove-described processing in steps S119 and S120 is referred to as theflickerless image capturing function. After a recording image iscaptured through the execution of the flickerless image capturingfunction in steps S119 and S120, the processing returns to steps S104and S109, respectively. Then, the CPU 104 restarts live view display.When no flicker is detected (DC in step S118), the processing proceedsto step S121. In step S121, the CPU 104 performs the main exposurewithout adjusting the timing of the exposure period. Then, theprocessing returns to step S114.

Although, in the descriptions above, the CPU 104 detects a peak timingof the light amount change of the flicker (at which the light amount ismaximized) and controls the exposure period of the image sensor 101based on the detected peak timing, the present invention is not limitedthereto. The flickerless image capturing function of the camera mainbody 100 according to the present embodiment may perform the mainexposure in accordance with the timing (bottom timing) at which thelight amount of the subject changing by the flicker is minimized.

As described above, the camera main body 100 according to the presentembodiment performs the flicker detection operation not only when theflicker detection operation is performed by the user but alsoimmediately before main image capturing for capturing a recording imageis performed. When a flicker is detected, the CPU 104 can suitably setthe charge accumulation period for reducing the influence of the flickerduring live view display after image capturing while executing theflickerless image capturing function in accordance with the featurepoint of the light amount change of the detected flicker.

The above-described flicker detection operation in steps S105, S110, andS115 has been an operation for directly issuing a flicker detectioninstruction. However, for example, the flicker detection operation maybe performed in association with an operation (instruction) for changingthe display content of the display 103.

(Flickerless Image Capturing Function During Live View Display)

The timing will be describe in detail below at which each operation isperformed in a case of performing flickerless image capturing duringlive view display according to the present embodiment. The basicoperation is based on the above-described processing according to theflowchart illustrated in FIG. 3. FIG. 7 illustrates a timing chartrelated to the flickerless image capturing operation during live viewdisplay according to the first embodiment of the present invention. Thetiming chart illustrated in FIG. 7 premises a case where live viewdisplay is started when power of the camera main body 100 is turned on.Each operation illustrated in FIG. 7 is performed when the camera mainbody 100 and each apparatus connected to the camera main body 100operate according to an instruction of the CPU 104. In the followingdescriptions, the description about the entity which performs eachoperation will be omitted.

Referring to FIG. 7, when power of the camera main body 100 is turned onto activate each part of the camera main body 100, the CPU 104 performsthe scan type photometry method (scan photometry) at the timing T1. Thescan photometry is a method for determining the optimum exposure byperforming photometry based on a plurality of images (signals) preparedin accordance with a plurality of predetermined exposures. Morespecifically, according to the present embodiment, the CPU 104 performsphotometry on a plurality of images captured with a predeterminedexposure by using the image sensor 101 (to calculate the luminancevalue) and calculates the difference value from a predetermined targetluminance value for each luminance value. The CPU 104 determines theoptimum exposure (proper exposure) to be used in the image acquisitionfor live view based on the combination of the calculated and the targetluminance values having the smallest absolute value of the differencetherebetween.

At the timing T2, the CPU 104 performs the flicker detection operation.At the timing T3, the CPU 104 display the live view on the display 103.In this case, when capturing the image to be used for live view display,the CPU 104 performs the exposure control based on the result of thescan photometry previously performed and the result of the flickerdetection to display the live view with the reduced influence of theflicker.

Subsequently, upon detection of the image pickup instruction issued whenthe user operates the image pickup instruction unit 110 during live viewdisplay, the CPU 104 interrupts the current live view display and, atthe timing T4, performs the flicker detection operation again. Then, atthe timing T5, the CPU 104 performs flickerless image capturing (mainimage capturing) based on the result of the flicker detection performedat the timing T4. The method for the flicker detection operation and themethod for flickerless image capturing are as described above, andredundant descriptions thereof will be omitted. In the flicker detectionoperation performed at the timing T4, the CPU 104 detects the lightamount change period and the flicker peak timing of the flicker (inaccordance with the presence or absence of a flicker).

The CPU 104 performs the flicker detection operation at the timing T4 ina case where the flickerless image capturing function is preset to ON inthe camera main body 100. Therefore, in a case where the flickerlessimage capturing function is preset to OFF, the CPU 104 performs subjectimage pickup (main subject image capturing) for capturing a still imagewhile omitting the flicker detection operation at the timing T4.

Upon completion of main image capturing, then at the timing T6, the CPU104 performs live view display on the display 103 again. In live viewdisplay at the timing T6, the CPU 104 performs the exposure controlbased on the result of the last flicker detection to perform live viewdisplay with the reduced influence of the flicker. More specifically, inthe camera main body 100 according to the present embodiment, theexposure control for live view display is updated based on the result ofthe flicker detection operation last performed. In other words, duringlive view display, the camera main body 100 according to the presentembodiment determines the exposure for live view display to reduce theinfluence of the flicker each time the flicker detection operation isnewly performed.

In the example case, at the timings T7 and T8, the user operates theimage pickup setting input unit 111 during live view display to issue amenu display instruction for displaying various setting items. In thiscase, the CPU 104 stops (interrupts) live view display upon issuance ofthe menu display instruction by the user and, at the timing T7, displaysan arbitrary menu (setting screen) according to a user's operation onthe display 103. Upon issuance of a menu display stop instruction by theuser, then at the timing T8, the CPU 104 performs live view displayagain.

The flicker detection operation when the live view mode is thesimulation mode will be described below. As described above, in theflicker detection operation according to the present embodiment, the CPU104 detects the presence or absence of a flicker, the light amountchange period, and a flicker peak timing. Therefore, the detectionaccuracy of the flicker detection operation degrades if saturated andunderexposure regions exist in the image to be used for the flickerdetection.

As an example situation where saturated and underexposure regions arelikely to occur, there is a case where the exposure conditions arechanged by a user's manual operation. This case is equivalent to a statewhere the exposure correction has been performed on the proper exposurepreviously acquired. When the live view mode is the simulation mode, theCPU 104 performs the flicker detection operation without reflecting theuser-set exposure correction to the control values (luminance values) asthe reference for the exposure control. In other words, even when thelive view mode is the simulation mode, the CPU 104 performs the exposurecontrol for the flicker detection operation regardless of the user-setexposure.

The luminance value to be used for the flicker detection operation iscalculated regardless of the preset photometry mode in order to preventthe photometry result from changing according to the photometry mode.Although, in the present embodiment, the CPU 104 uses the averageluminance value as a result of performing photometry on the entire imageon an average basis, the CPU 104 may use the average luminance valuebased on the output of the region to be used for the flicker detectionoperation.

As described above, to prevent the occurrence of saturated andunderexposure regions, it is preferable to perform the flicker detectionoperation without reflecting the exposure correction. However, inparticular, in order to accurately detect the peak timing in the flickerdetection operation, it is desirable to reduce saturated regions as muchas possible. Accordingly, in the camera main body 100 according to thepresent embodiment, the CPU 104 detects saturated regions with referenceto a luminance-related histogram. If saturated regions are detected, theCPU 104 may set the exposure in the flicker detection operation toreduce the influence of the saturation.

Summarizing the above-described configuration, the CPU 104 acquires theluminance value to be used for the exposure control for live viewdisplay according to the preset photometry mode. In this case, when thelive view mode is the simulation mode, the CPU 104 performs the exposurecontrol for live view in accordance with the user-set exposureconditions (more specifically, the CPU 104 shifts the luminance value tobe used for the exposure control by the amount corresponding to theexposure correction). On the other hand, in the flicker detectionoperation, the CPU 104 calculates the luminance value by using apredetermined method regardless of the preset photometry mode and thelive view mode, and performs the exposure control when capturing animage for flicker detection based on the luminance value. The CPU 104detects saturated and underexposure regions based on a luminancehistogram when calculating the luminance value for flicker detectionoperation. If saturated and underexposure regions are detected, the CPU104 corrects the luminance value to reduce the saturated andunderexposure regions.

Processing based on the timing chart illustrated in FIG. 7 will bedescribed below with reference to the flowcharts illustrated in FIGS. 8and 9. The flowcharts illustrated in FIGS. 8 and 9 premise a case wherethe flickerless image capturing function is preset to ON in the cameramain body 100 and where live view display is started when power of thecamera main body 100 is turned on. FIG. 8 is a flowchart illustratingprocessing related to the flicker detection operation during live viewdisplay according to the first embodiment of the present invention.

When the CPU 104 starts live view display processing upon issuance of alive view start instruction (turning on power of the camera main body100 or other operations for starting the live view), then in step S201,the CPU 104 performs the scan photometry and calculates the exposureconditions for achieving the proper exposure.

In step S202, the CPU 104 performs the flicker detection operation. Instep S203, the CPU 104 performs the exposure control based on the resultof the flicker detection in step S202 and, based on the exposureconditions for reducing the influence of the flicker, starts live viewdisplay on the display 103.

In step S204, the CPU 104 determines whether the user performs anoperation requiring to stop (interrupt) live view display (live viewstop operation). When the CPU 104 determines that the user performs alive view stop operation (YES in step S204), the processing proceeds tostep S205. In step S205, the CPU 104 stops (interrupts) the current liveview display. On the other hand, when the CPU 104 determines that theuser does not perform a live view stop operation (NO in step S204), theprocessing repeats step S204.

Live view stop operations include a subject image pickup instruction, amenu display instruction, and an image reproduction instruction.Although the above-described flicker detection operation is alsoincluded in live view stop operations, the live view is subjected to aframe stop when a flicker detection operation instruction is issued.More specifically, a live view stop operation according to the presentembodiment is an operation for stopping either the acquisition of animage for live view or the update of the live view image currentlydisplayed on the display 103.

The following descriptions will be made on the premise that the liveview stop operation determined in step S204 is a subject image pickupinstruction. FIG. 9 is a flowchart illustrating image capturingprocessing during live view display according to the first embodiment ofthe present invention. After live view display is stopped, then in stepS301, the CPU 104 performs the flicker detection operation to detect thepresence or absence of a flicker, the light amount change period, andthe flicker peak timing.

In step S302, the CPU 104 performs main image capturing based on theresult of the flicker detection in step S301 and the previously acquiredinformation about the proper exposure to capture a still image(recording image). When a flicker is detected in step S301, the CPU 104performs image capturing (flickerless image capturing) in accordancewith the flicker peak timing. On the other hand, when no flicker isdetected in step S301, the CPU 104 performs image pickup regardless ofthe flicker peak timing.

In step S303, the CPU 104 determines whether the image pickupinstruction by the user is continued, and a continuous image capturinginstruction is issued. When the CPU 104 determines that the continuousimage capturing instruction is issued (YES in step S303), the processingreturns to step S301. The CPU 104 performs the flicker detection again.When the CPU 104 determines that the continuous image capturinginstruction is not issued (NO in step S303), the CPU 104 ends the imagecapturing processing. In this case, the processing returns to step S203illustrated in FIG. 8, and the CPU 104 resumes live view display.

If the flicker detection operation between continuous image capturingframes is configured to detect only the peak timing without detectingthe light amount change period of the flicker, the continuous framecapturing frame rate (interval of continuous main image capturing) canbe reduced. This is because the probability that the light amount changeperiod of the flicker changes is low in a short period during continuousimage capturing. On the contrary, it is desirable to detect the flickerpeak timing each time the CPU 104 performs subject image capturing. Thisis because the peak of the light amount gradually changes because of aminute deviation from a theoretical value of the commercial powerfrequency. The flicker peak timing can be detected based on a pluralityof images equivalent to one light amount change period of the flicker.Therefore, the CPU 104 needs to drive the image sensor 101 at 600 fpsand repeat a cycle of the charge accumulation and readout operations sixtimes, thus capturing the plurality of the images. When the preventionof the frame rate reduction is given priority in continuous imagecapturing, the CPU 104 may not perform the flicker detection operationfor each image pickup in continuous image capturing.

When the live view stop operation determined in step S204 is a menudisplay instruction or an image reproduction instruction, the CPU 104may determine, in processing newly provided, whether an instruction forcontinuing menu display and image reproduction is issued. When thecontinuation instruction is not issued, the processing returns to stepS203. In addition, when the live view stop operation determined in stepS204 is a flicker detection operation, the CPU 104 may determine, inprocessing newly provided, whether the instruction for the flickerdetection operation by the user is continued. When the instruction isnot continued, the processing returns to step S203. In either case, thecamera main body 100 is configured to perform the exposure control forlive view display based on the latest flicker detection result.

The camera main body 100 according to the present embodiment can performthe flicker detection operation regardless of the ON/OFF state of theflickerless image capturing function. More specifically, according tothe present embodiment, when live view display is started, the CPU 104performs the flicker detection operation (step S102) even when theflickerless image capturing function is OFF. This processing is intendedto prevent the quality of live view display from being degraded by theinfluence of a flicker when live view display is started. The flickerdetection operation (steps S105, S110, and S115) by the user request canbe performed even when the flickerless image capturing function is OFF.This aims for reducing the possibility that image capturing is performedin a state where the presence or absence of a flicker cannot bedetermined. This configuration enables the user to easily determine thepresence or absence of a flicker without changing the image capturingfunction. On the contrary, according to the present embodiment, toprevent the increase in the release time lag, the CPU 104 does notperform the flicker detection operation (S118) according to the user'simage capturing operation when the flickerless image capturing functionis OFF.

An image pickup system according to a second embodiment of the presentinvention will be described below with reference to FIGS. 10 to 13. Thebasic configuration of the image pickup system centering on the cameramain body 100 is almost identical to that according to theabove-described first embodiment, and redundant descriptions thereofwill be omitted. The present embodiment differs from the firstembodiment in the exposure control method related to the flickerdetection operation.

FIG. 10 is a flowchart illustrating flickerless image capturingprocessing in a case where the flickerless image capturing function isON, according to the second embodiment of the present invention. FIG. 10is a flowchart illustrating various types of processing on theassumption of a case where main image capturing is performed during liveview display. When power of the camera main body 100 is turned on, thenin step S401, the CPU 104 captures an image by using the image sensor101 and performs the photometry operation based on the image tocalculate a photometry value BvAve.

FIG. 11 illustrates a method for calculating, when a flicker exists, thephotometry value (luminance value) in accordance with the light amountchange period of the flicker. To prevent unevenness in brightness in animage because of the influence of the flicker, the charge accumulationperiod of the image sensor 101 is made longer than one light amountchange period of the flicker when capturing a live view image. Thephotometry value acquired in this case is an average photometry valueBvAve as a result of averaging the light amount changes by the flicker,as illustrated in FIG. 11.

In step S402, the CPU 104 determines whether an image pickup instructionis issued by a user request. When an image pickup instruction is notdetected (NO in step S402), the processing returns to step S401. On theother hand, when an image pickup instruction is issued (YES in stepS402), the processing proceeds to step S403.

In step S403, the CPU 104 performs the flicker detection operation byusing a method similar to that in the above-described first embodimentto determine whether a flicker is detected. When a flicker is detected(FLICKER DETECTED in step S403), the processing proceeds to step S404.In step S404, the CPU 104 calculates an exposure correction amount Compaccording to the light amount change period of the flicker and theexposure time in image pickup. The following describes the necessity ofcorrecting the photometry value when a flicker is detected, withreference to FIG. 12. FIG. 12 illustrates a relation between the lightamount change period of the flicker and the exposure time.

As described above, in flickerless image capturing, the CPU 104 sets theexposure period by using the image sensor 101 based on the flicker peaktiming. When the exposure time is short (i.e., in short-time imagecapturing at a high shutter speed), the light amount in the vicinity ofthe flicker peak timing is averaged. In this case, a luminance valueBvStil corresponding to the exposure time in image capturing becomesmore overexposure than the average photometry value BvAve. Therefore,the image brightness will become unnatural even if the CPU 104 performssubject image capturing under the exposure conditions set in accordancewith the average photometry value BvAve.

According to the present embodiment, to prevent the brightness of animage captured in flickerless image capturing from becoming unnatural,the CPU 104 corrects the photometry value based on the exposurecorrection amount Comp in accordance with the exposure time in imagepickup. The difference between the luminance value and the averagephotometry value BvAve corresponding to the exposure time in imagecapturing decreases with increasing exposure time. Therefore, thepresent embodiment is configured to achieve the optimum exposureaccording to the exposure time by using the variable exposure correctionamount Comp. FIG. 13 illustrates a method for calculating an exposurecorrection amount according to the second embodiment of the presentinvention.

In step S405, the CPU 104 calculates the shutter speed (exposure time)Tv, the aperture value Av, and the ISO sensitivity as exposureconditions for main image capturing based on the photometry value BvAveacquired in step S401. The photometry value Bv to be used whencalculating these exposure conditions is calculated based on thefollowing Formula (2).Bv=BvAve+Comp(X)  (2)

(X) is determined according to the value of the shutter speed (exposuretime) Tv based on the data illustrated in FIG. 13. In step S406, forreference in the subsequent processing, the CPU 104 stores the exposurecorrection amount Comp(X) under an alias LastComp in a predeterminedarea of the recording unit 112. In step S407, the CPU 104 performs mainimage capturing under the exposure conditions based on the exposurecorrection amount calculated in step S404, to capture a still image(recording image). When a flicker is detected, the CPU 104 performssubject image capturing in accordance (synchronization) with the flickerpeak timing (flickerless image capturing). On the other hand, when aflicker is not detected, the CPU 104 performs subject image capturingregardless of the flicker peak timing.

In step S408, the CPU 104 determines whether the image pickupinstruction (image capturing request) from the user is continued. Whenthe image pickup instruction is continued (YES in step S408), theprocessing proceeds to step S409. On the other hand, when the CPU 104determines that the image pickup instruction is not continued (NO instep S408), the CPU 104 ends a series of the image capturing processing.

In step S409, the CPU 104 calculates the photometry value based on therecording image (still image) previously captured in the main imagecapturing and stores the photometry value as a photometry value Bv1. Instep S410, the CPU 104 performs the flicker detection operation. Asdescribed above in the first embodiment, the CPU 104 may perform onlythe peak timing detection in the flicker detection operation in stepS410.

When a flicker is detected (FLICKER DETECTED in step S410), theprocessing proceeds to step S411. In step S411, the CPU 104 calculatesthe exposure correction amount Comp. On the other hand, when no flickeris detected (NO FLICKER in step S410), the processing proceeds to stepS412.

The exposure correction amount Comp calculated in step S411 is theexposure correction amount for the averaged photometry value BvAve.Therefore, if the photometry value is calculated by Bv=Bv1+Comp(X), likethe Formula (2) based on the exposure correction amount, the exposurecorrection will be performed in a duplicated way. More specifically, thephotometry value Bv1 is calculated based on an image captured in a statewhere the average photometry value BvAve is corrected based on theexposure correction amount LastComp in the last main image capturing.Therefore, the exposure correction will be performed in a duplicatedway.

According to the present embodiment, therefore, to remove the influenceof the exposure correction amount LastComp in the last main imagecapturing, in step S412, the CPU 104 calculates the photometry value Bybased on the following Formula (3).Bv=Bv1−LastComp+Comp(X)  (3)

Even when performing continuous image capturing in flickerless imagecapturing during live view display, this configuration makes it possibleto prevent the exposure correction from being performed in a duplicatedway in the second and subsequent image pickups.

Processing in subsequent steps S413 to S414 is identical to theprocessing in steps S406 to S407, respectively, redundant descriptionsthereof will be omitted. When the image pickup instruction is continued(YES in step S408), the CPU 104 repeats the processing in steps S409 toS414. When no flicker is detected in the flowchart illustrated in FIG.10, the CPU 104 needs to perform each piece of processing assuming thatthe exposure correction amount Comp and the last exposure correctionamount LastComp are zero.

According to the present embodiment, adopting the above-describedconfiguration enables the camera main body 100 to effectively preventfrom becoming unnatural the brightness of an image captured throughsubject image capturing when performing flickerless image capturingduring live view display.

An image pickup system according to a third embodiment of the presentinvention will be described below with reference to FIGS. 14A to 16B.The basic configuration of the image pickup system centering on thecamera main body 100 is almost identical to that of the above-describedfirst embodiment, and redundant descriptions thereof will be omitted.The present embodiment differs from the above-described first embodimentin the flicker detection operation for each of lenses with differentaperture drive methods.

An absolute aperture drive and a relative aperture drive as aperturecontrol for each lens according to the present embodiment will bedescribed below. The absolute aperture drive refers to control in which,when driving the aperture up to a certain target aperture value, it isnecessary to once set the open area amount of the aperture 202 to amaximum aperture before driving the aperture 202 up to the open areaamount corresponding to the target aperture value. This control isperformed for the following reason. In terms of the aperture stopaccuracy, the aperture drive accuracy can be stably maintained by onceopening the aperture and then driving the aperture up to the targetvalue, because of the influence of inverting backlash arising whenchanging the aperture drive direction.

On the other hand, the relative aperture drive refers to control inwhich, when driving the aperture up to a certain target aperture value,it is not necessary to once open the aperture before driving theaperture until the open area amount corresponding to the target aperturevalue is achieved. In the relative aperture drive, the imaging lensprestores correction data for reducing inverting backlash. Therefore, interms of the aperture stop accuracy, the aperture accuracy can be stablymaintained, without once opening the aperture, by correcting theaperture drive based on the correction data. For details on thecorrection data, any known technique may be used to correct the aperturedrive.

FIG. 14 is a flowchart illustrating image capturing processing forperforming the flicker detection during live view display according tothe third embodiment of the present invention. For processing identicalto the image capturing processing illustrated in FIG. 3 according to theabove-described first embodiment, out of processing illustrated in FIG.14, redundant descriptions will be omitted.

Processing in steps S501 to S503 is identical to the processing in stepsS101 to S102 and step S104, S109, or S114 in the above-described firstembodiment, and redundant descriptions thereof will be omitted. Like theabove-described first embodiment, in step S503, the exposure time (orcharge accumulation period) when capturing an image for live view basedon the result of the flicker detection processing in step S502 isdifferent. During live view display, the CPU 104 performs the photometryoperation at predetermined intervals based on the image for live view tosuitably control the exposure conditions for the live view image.

In step S504, the CPU 104 determines whether an image pickup instructionis issued upon execution of an image capturing operation by the user(for example, on the image pickup instruction unit 110). When the CPU104 determines that the image pickup instruction is not issued (NO instep S504), the processing returns to step S503. On the other hand, whenthe CPU 104 determines that the image pickup instruction is issued (YESin step S504), the processing proceeds to step S505.

In step S505, the CPU 104 performs the exposure control for flickerdetection with the current aperture value setting given priority. In theprocessing in step S505, the CPU 104 performs the exposure control withthe current aperture given priority based on the photometry result forthe image for live view captured in step S503 or the photometry resultfor the recording image (still image) to be captured in step S519(described below). More specifically, in step S505, the CPU 104calculates the exposure conditions when performing the flicker detectionoperation with the current state of the aperture 202 (i.e., currentaperture value) given priority.

As described above in the first embodiment, in the flicker detectionoperation, the CPU 104 drives the image sensor 101 to continuouslyperform the accumulation and readout operations at 600 fps, i.e., atintervals of about 1.667 milliseconds (for example, 12 times). The CPU104 performs these continuous accumulation operations under the sameexposure conditions. For example, if the current aperture value is anextremely large value (i.e., small aperture), the proper exposure maynot be achieved with an exposure time (charge accumulation period) of1.667 milliseconds even with a large ISO sensitivity. In this case,since the accumulation operation is performed at 1.667-ms intervals, adark image not suitable for the flicker detection will be captured.Alternatively, even if an image is captured with an exposure time longerthan 1.667 milliseconds, the flicker detection cannot be accuratelyperformed based on this image. In such a case, since the flickerdetection cannot be performed if the aperture value remains unchanged,the exposure conditions allowing the flicker detection operation cannotbe set with the current aperture fixed. Therefore, in such a case, theCPU 104 calculates the exposure conditions accompanied by the change ofthe current aperture value as exposure conditions for flicker detection.

In step S506, based on the result of the calculation in step S505, theCPU 104 determines whether the flicker detection operation can beperformed without changing the current aperture value of the aperture202. More specifically, in step S506, if the flicker detection operationcannot be accurately performed without changing the current aperturevalue based on the calculation result in step S505, the CPU 104determines that the flicker detection cannot be performed with thecurrent aperture value. When the CPU 104 determines that the flickerdetection can be performed with the current aperture value (YES in stepS506), the processing proceeds to step S510. On the other hand, when theCPU 104 determines that the flicker detection cannot be performed withthe current aperture value (NO in step S506), the processing proceeds tostep S507.

In step S507, based on the in-focus position and lens information (forexample, lens identifier (ID)) acquired by communicating with the LPU203, the CPU 104 determines whether the imaging lens 200 attached to thecamera main body 100 is a lens with the relative aperture drive. Whenthe CPU 104 determines that the imaging lens 200 is a lens with therelative aperture drive (YES in step S507), the processing proceeds tostep S509. On the other hand, when the CPU 104 determines that theimaging lens 200 is not a lens with the relative aperture drive (NO instep S507), i.e., the imaging lens 200 is a lens with the absoluteaperture drive, the processing proceeds to step S508. The relativeaperture drive and the absolute aperture drive for the imaging lens 200will be described in detail below with reference to FIGS. 15A, 15B, 16A,and 16B.

Since the imaging lens 200 is a lens with the absolute aperture drive,then in step S508, the CPU 104 drives the opening of the aperture 202 tothe open position. Then, the processing proceeds to step S509. In stepS509, using the aperture value calculated in step S505 as a targetvalue, the CPU 104 drives the aperture 202 by using the aperture driveunit 205 to achieve the open area amount corresponding to the targetvalue.

Processing in step S510 is identical to the processing in step S118according to the above-described first embodiment, and redundantdescriptions thereof will be omitted. In step S511, the CPU 104calculates the exposure conditions for main image capturing based on thephotometry result for the live view image captured in step S503.Processing in steps S512 to S514 is almost identical to the processingin steps S507 to S509, respectively, and redundant descriptions thereofwill be omitted. In the processing in steps S512 to S514, the targetaperture value is the aperture value for main image capturing calculatedin step S511.

Processing in step S515 is identical to the processing in step S119,S120, or S121 according to the above-described first embodiment, andredundant descriptions thereof will be omitted. Only when a flicker isdetected, the CPU 104 performs main image capturing (flickerless imagecapturing) in synchronization with the flicker peak timing. On the otherhand, when no flicker is detected, the CPU 104 performs main imagecapturing regardless of the flicker peak timing.

In step S516 (like steps S507 and S512), the CPU 104 determines whetherthe imaging lens 200 is a lens with the relative aperture drive. Whenthe imaging lens 200 is a lens only with the absolute aperture drive,the CPU 104 drives the aperture 202 to the open position after mainimage capturing. This processing is intended to save the time and effortto drive the aperture 202 to the open position in the next andsubsequent main image capturing to reduce the release time lag.Processing in step S517 is identical to the processing in steps S509 andS513, and redundant descriptions thereof will be omitted.

In step S518, the CPU 104 determines whether the image pickupinstruction by the user is continued. More specifically, in step S518,the CPU 104 determines whether image capturing is completed. When theCPU 104 determines that image capturing is completed (YES in step S518),the CPU 104 ends the image capturing processing. On the other hand, whenthe CPU 104 determines that image capturing is not completed (NO in stepS518), the processing proceeds to step S519. In step S519, the CPU 104performs the photometry processing based on the recording image (stillimage) captured in main image capturing in step S515. Then, theprocessing returns to step S505, and the CPU 104 repeats the processingin step S505 and the subsequent processing.

The above-described image capturing processing when the imaging lens 200is a lens with the absolute aperture drive and image capturingprocessing when the imaging lens 200 is a lens with the relativeaperture drive will be described below with reference to the timingcharts illustrated in FIGS. 15A, 15B, 16A, and 16B. FIGS. 15A and 15Billustrate timing charts and aperture states related to the flickerlessimage capturing processing for each of lenses with different aperturedriving methods according to the third embodiment of the presentinvention. FIG. 15A illustrates an operation when the imaging lens 200is a lens with the absolute aperture drive, and FIG. 15B illustrates anoperation when the imaging lens 200 is a lens with the relative aperturedrive.

Referring to FIGS. 15A and 15B, the CPU 104 performs similar processingat similar timings since the time Ta0 and Tb0 when power of the cameramain body 100 is turned on till the time Ta1 and Tb1 when the exposurecalculation for main image capturing is completed.

The following describes operations when the imaging lens 200 is a lenswith the absolute aperture drive. Referring to FIG. 15A, at the time Ta1when the exposure calculation for main image capturing is completed, theCPU 104 starts the drive of the aperture 202 to the open position. Then,the CPU 104 completes the drive of the aperture 202 to the target valueby the time Ta2. Since the time Ta2 to till the time Ta3, the CPU 104performs the accumulation (exposure) operation for main image capturing.Between the time Ta3 and Ta4, the CPU 104 reads the image signalcorresponding to the last accumulation operation and parallelly drivesthe aperture 202 to the open position again. This is because, asdescribed above, it is necessary to open the aperture 202 for thefollowing image capturing.

When the image pickup instruction by the user is continued, then at thetime Ta5, the CPU 104 performs the exposure calculation for flickerdetection by giving priority to the aperture value (open aperture value)for a state where the aperture 202 is at the open position to performflicker detection. Since the present embodiment is based on an examplecase where the flicker detection operation is possible with the openaperture value, the drive operation of the aperture 202 does not occurat this timing. At the time Ta6 when the exposure calculation for mainimage capturing is completed, the CPU 104 starts the drive of theaperture 202. When the drive of the aperture 202 to the target value iscompleted, the CPU 104 performs the following image capturing (stillimage capturing). Subsequently, the CPU 104 repeats these operationswhile the image pickup instruction is continued.

The following describes operations when the imaging lens 200 is a lenswith the relative aperture drive. Referring to FIG. 15B, at the time Tb1when the exposure calculation for main image capturing is completed, theCPU 104 starts the drive of the aperture 202. Then, the CPU 104continues the drive of the aperture 202 up to the target aperture valuefor main image capturing till the time Tb2, without driving the aperture202 to the open position. Since the time Tb2 till the time Tb3, the CPU104 performs the accumulation (exposure) operation for main imagecapturing. Then, the CPU 104 cancels the drive of the aperture 202leaving the aperture value unchanged without driving the aperture 202.This is because, when the imaging lens 200 is a lens with the relativeaperture drive, it is not necessary to leave the aperture 202 open inaccordance with the following main image capturing.

When the image pickup instruction by the user is continued, then at thetime Tb5, the CPU 104 performs the exposure calculation for flickerdetection with the current aperture value given priority to perform theflicker detection. Since the present embodiment is based on an examplecase where the flicker detection operation remains possible with thecurrent aperture value, the drive operation of the aperture 202 does notoccur at this timing. At the time Tb6 when the exposure calculation formain image capturing is completed again, the CPU 104 starts the drive ofthe aperture 202 to perform the following main image capturing (stillimage capturing). Subsequently, the CPU 104 repeats these operationswhile the image pickup instruction is continued.

FIGS. 16A and 16B illustrate timing charts and aperture states relatedto a case of driving the aperture 202 in the flicker detection operationfor each of lenses with different aperture driving methods according tothe third embodiment of the present invention. FIG. 16A illustrates anoperation when the imaging lens 200 is a lens with the absolute aperturedrive, and FIG. 16B illustrates an operation when the imaging lens 200is a lens with the relative aperture drive.

The following describes operations when the imaging lens 200 is a lenswith the absolute aperture drive, with reference to FIG. 16A. Theoperations up to the first main image capturing are identical to theabove-described operations illustrated in FIG. 15A, and redundantdescriptions thereof will be omitted. As illustrated in FIG. 16A, at thetime Tc0 when main image capturing is completed, the CPU 104 performsthe exposure calculation for flicker detection with the open aperturevalue given priority. Since the exposure conditions provide excessivebrightness to the subject, there assumes a case where the flickerdetection cannot be performed with the open aperture value.

In this case, at the time Tc1, the CPU 104 starts the drive of theaperture 202 to the open position. Then, the CPU 104 completes the driveof the aperture 202 by the time Tc2 when the flicker detection operationis started. At the time Tc2, the CPU 104 performs the flicker detectionoperation. Between the time Tc3 and Tc4, the CPU 104 drives the aperture202 again to the open position. As described above, this is the aperturedrive operation for the following image capturing. Then, at the time Tc5when the exposure calculation for main image capturing is completed, theCPU 104 starts the drive of the aperture 202. Upon completion of thedrive of the aperture 202, the CPU 104 performs the following main imagecapturing (still image capturing). Subsequently, the CPU 104 repeatsthese operations while the image pickup instruction is continued.

The following describes operations when the imaging lens 200 is a lenswith the relative aperture drive, with reference to FIG. 16B. Theoperations up to the first main image capturing are identical to theabove-described operations illustrated in FIG. 15B, and redundantdescriptions thereof will be omitted. As illustrated in FIG. 16B, at thetime Td1 when main image capturing is completed, the CPU 104 performsthe exposure calculation for flicker detection with the current aperturevalue given priority. Since the exposure conditions provide excessivedarkness to the subject, there assumes a case where the flickerdetection cannot be performed with the current aperture value.

In this case, the CPU 104 starts the drive of the aperture 202 at thetime Td2 and continues the drive of the aperture 202 till the time Td3when the aperture value allowing the flicker detection operation isachieved. After performing the flicker detection operation at the timeTd3, the CPU 104 does not drive the aperture 202 but stops the drive ofthe aperture 202 leaving the aperture value unchanged. This is because,since the relative aperture drive is possible, it is not necessary todrive the aperture 202 to the open position for the following imagecapturing. Then, at the time Td5 when the exposure calculation for mainimage capturing is completed, the CPU 104 starts the drive of theaperture 202 in accordance with the aperture value for main imagecapturing. Upon completion of the drive of the aperture 202, the CPU 104performs the following main image capturing (still image capturing).Subsequently, the CPU 104 repeats these operations while the imagepickup instruction is continued.

As described above, the camera main body 100 and the imaging lens 200according to the present embodiment enables the optimum aperture drivein accordance with the flicker detection and the flickerless imagecapturing operation according to the type of the imaging lens 200. Morespecifically, regardless of the lens type, the CPU 104 determineswhether the flicker detection operation is possible with the currentaperture value. According to the result of the determination, the CPU104 performs control to perform the optimum aperture drive according tothe presence or absence of the aperture drive and the type of theimaging lens 200. This configuration makes it possible to accuratelyperform the flicker detection operation regardless of the type of theimaging lens 200, and quickly perform the flicker detection operationand flickerless image capturing according to the type of imaging lens200.

The following describes the image pickup system according to the thirdembodiment of the present invention, with reference to FIGS. 17 to 19.The basic configuration of the image pickup system centering on thecamera main body 100 is almost identical to that of the above-describedfirst embodiment, and redundant descriptions thereof will be omitted.The present embodiment will be specifically described below centering ona case where the CPU 104 performs light emission image capturing byusing the built-in stroboscope 114 or the external stroboscope 300 inaddition to the flicker detection operation during live view displayaccording to the above-described first embodiment.

FIG. 17 is a flowchart illustrating flicker detection processing inlight emission image capturing according to a fourth embodiment of thepresent invention. The flowchart illustrated in FIG. 17 indicates imagecapturing preparation processing performed during the time period sincethe time when an image pickup instruction is issued by the user till thetime when main image capturing is performed assuming a case whereflickerless image capturing is performed during live view display. Forexample, according to the above-described first embodiment, the imagecapturing preparation processing corresponds to the processing in stepS118 illustrated in FIG. 3.

In step S601, the CPU 104 determines whether the setting in lightemission image capturing is the multi-light emission mode using aplurality of light emitting devices. The multi-light emission mode is alight emission mode in which a subject is illuminated by a plurality oflight emitting devices and light emission image capturing is performedin main image capturing. When the multi-light emission mode is enabled(ON), the CPU 104 performs, immediately before main image capturing,pre-light emission by using a plurality of light emitting devicesdivided into a plurality of light emission groups and performs lightamount control calculation for calculating the main light emissionamount. When the CPU 104 determines that the setting in light emissionimage capturing is not the multi-light emission mode (NO in step S601),the processing proceeds to step S602. On the other hand, when the CPU104 determines that the setting in light emission image capturing is themulti-light emission mode (YES in step S601), the processing proceeds tostep S605.

In step S602, the CPU 104 performs the flicker detection operation and,particularly at this timing, detects at least the flicker peak timing.The flicker detection operation method according to the presentembodiment is identical to that according to the above-described firstembodiment, and redundant descriptions thereof will be omitted.

In step S603, the CPU 104 performs the aperture control for main imagecapturing (image capturing aperture control). In this case, immediatelybefore main image capturing, the CPU 104 adjusts the aperture diameterof the aperture 202 to achieve the aperture value for main imagecapturing based on the aperture value for live view display. Morespecifically, the CPU 104 transmits an aperture change request to theLPU 203 of the imaging lens 200 and controls the aperture drive unit 205according to an instruction of the LPU 203 to change the open areaamount (aperture position) of the aperture 202.

In step S604, the CPU 104 performs pre-light emission using a lightemitting device and, based on the result of pre-light emission,calculates the light emission amount (main light emission amount) inmain image capturing (light amount control calculation). The lightemitting device in step S604 is assumed to be the external stroboscope300. In the processing in step S604, before main image capturing, theCPU 104 issues a pre-light emission instruction based on a predeterminedlight emission amount to the SPU 301 included in the externalstroboscope 300. Then, the CPU 104 calculates the main light emissionamount based on images captured by performing subject image capturing inpre-light emission according to the preliminary light emissioninstruction. As described above, in a case where multi-light emission isnot performed by the light emitting device, the CPU 104 performsoperations in order of the flicker peak timing detection, the imagecapturing aperture control, and the pre-light emission.

As the method for calculating the main light emission amount accompaniedby pre-light emission (light amount control calculation), any knownmethods are applicable. According to the present embodiment, the CPU 104compares a non-light emission image captured in the non-light emissionstate of the light emitting device with a pre-light emission imagecaptured in the pre-light emission state of the light emitting device tocalculate the reflected light component of the subject, and calculatesthe main light emission amount by associating prestored data with thecalculated reflected light component.

Although, in the present embodiment, the CPU 104 performs the lightamount control calculation to calculate the main light emission amountat the timing when the non-light emission image and all pre-lightemission images are captured (for example, after step S604 and stepsS606 and S612 (described below)), the present invention is not limitedthereto. For example, if the light amount control calculation can becompleted before main image capturing, it is not necessary to performthe light amount control calculation immediately after completion ofpre-light emission. The timings of pre-light emission image acquisitionand the light amount control calculation may be timings other than theabove-described configuration.

When the CPU 104 determines that the setting in light emission imagecapturing is the multi-light emission mode (YES in step S601), theprocessing proceeds to step S605. In step S605, the CPU 104 determineswhether face region detection processing (face detection) is currentlybeing performed. In face detection, the CPU 104 applies pattern matchingpredetermined based on the image for live view display and detectswhether a face region is included in the image. In other words,performing the face detection enables determining whether the imagepickup target subject is a person or an object other than a person. Inface detection, the CPU 104 determines whether the subject is a personbased on the evaluation value for evaluating the degree of matching witha pattern indicating the face region prestored in the camera main body100.

When the CPU 104 determines that the face detection is not currentlybeing performed (NO in step S605), the processing proceeds to step S606.On the other hand, when the CPU 104 determines that the face detectionis currently being performed (YES in step S605), the processing proceedsto step S609. Processing in steps S606 to S612 corresponds to theprocessing for the multi-light emission mode.

In step S606, the CPU 104 performs pre-light emission by each lightemission group of the light emitting devices to be used for multi-lightemission and calculates the main light emission amount. The lightemitting device included in a master stroboscope in the multi-lightemission mode is the external stroboscope 300. A plurality of lightemitting devices as other slave stroboscopes has a configuration almostidentical to that of the external stroboscope 300. Communication(synchronization) control with an electric wave or light is possible forthese light emitting devices. In the multi-light emission mode, thepre-light emission timing is differentiated for each light emissiongroup.

Processing in subsequent steps S607 to S608 is identical to theprocessing in steps S602 to S603, and redundant descriptions thereofwill be omitted. As described above, in a case where multi-lightemission is performed by the light emitting device and face detection isnot performed, the CPU 104 calculates the main light emission amount inthe multi-light emission mode, detects the flicker peak timing, andfinally performs the image capturing aperture control.

When the CPU 104 determines that the setting in light emission imagecapturing is the multi-light emission mode (YES in step S601) and thatface detection is currently being performed (YES in step S605), theprocessing proceeds to step S609. In step S609, the CPU 104 performspre-light emission by each light emission group in the multi-lightemission mode and calculates the main light emission amount. However,unlike step S606, the CPU 104 does not perform pre-light emission forthe group including the external stroboscope 300 directly attached tothe camera main body 100. This is because the pre-light emission timingis differentiated between a light emission group performing front lightemission and the other light emission groups, assuming that a subject ismost likely to be illuminated from the front by a light emitting devicedirectly attached to the camera main body 100. In the followingdescriptions, the light emission group including the light emittingdevice performing front light emission is referred to as a masterstroboscope (group).

Processing in steps S610 and S611 is identical to the processing insteps S602 and S603, respectively, and redundant descriptions thereofwill be omitted. Finally, in step S612, the CPU 104 performs pre-lightemission by the group including the external stroboscope 300 directlyattached to the camera main body 100 and calculates the main lightemission amount in main image capturing.

The following describes the timing chart of each operation in theflowchart illustrated in FIG. 17, with reference to FIGS. 18A, 18B, and18C. FIGS. 18A, 18B, and 18C are timing charts illustrating flickerdetection processing in light emission image capturing according to thefourth embodiment of the present invention. Referring to FIGS. 18A, 18B,and 18C, “VD” indicates the timing of a vertical synchronization signalto be applied to the image sensor 101. The time period since the signalis once set to the Low level until it falls to the Low level again isthe period required to capture an image for one frame of the live view.“APERTURE POSITION” is a visual form of the open area amount of theaperture 202. The upper position is closer to the opening state. “LIGHTEMISSION TIMING” indicates, for example, the light emission timing ofthe illumination light using a light emitting device such as theexternal stroboscope 300. The CPU 104 reads output signals of pixelsconfiguring the image sensor 101 in synchronization with VD and repeatsthe control for resetting the integration value upon completion ofsignal readout, thus detecting changes of the luminance value of thesubject.

FIG. 18A illustrates various control timings related to the flickerdetection operation, the aperture drive, and the light emissionoperation of the light emitting device when the multi-light emissionmode is disabled (OFF) (NO in step S601). In a situation as illustratedin FIG. 18A, the CPU 104 performs the flicker detection operation.Details of the flicker detection operation are as described above in thefirst embodiment, and redundant descriptions thereof will be omitted. VDis issued in accordance with the 600-fps drive period of the imagesensor 101. The CPU 104 performs the flicker detection operation basedon the result of integrating a total of 12 outputs.

Then, the CPU 104 performs control to change the aperture value from theaperture value (f1.8) for live view display (flicker detection) to theaperture value (f5.6) for main image capturing, and at the same timechanges the drive control on the image sensor 101 for light amountcontrol. Finally, the CPU 104 performs pre-light emission and calculatesthe main light emission amount based on the integration result (lightamount control calculation). In the above-described control, when themulti-light emission setting is disabled (OFF) (i.e., when performingsingle light emission by a light emitting device), the CPU 104 performspre-light emission immediately before image capturing after the aperturedrive out of various control operations. This makes it possible toperform image capturing while preventing person's eye shutting.

FIG. 18B illustrates various control timings related to the flickerdetection operation, the aperture drive, and the light emissionoperations by the light emitting devices when the multi-light emissionmode is enabled (ON) and face detection is not currently being performed(NO in step S605).

In a situation as illustrated in FIG. 18B, the CPU 104 performspre-light emission by each light emission group of a plurality of lightemitting devices (slave stroboscopes EGr to BGr and master stroboscopeAGr) performing multi-light emission, and calculates the main lightemission amount based on the integration result (light amount controlcalculation). Then, the CPU 104 changes the drive control of the imagesensor 101 to the drive control for flicker detection and performs theflicker detection operation. Upon completion of the flicker detectionoperation, the CPU 104 changes the aperture value from the aperturevalue for live view display (flicker detection) to the aperture valuefor main image capturing. This configuration, in which the flickerdetection operation is performed immediately before main imagecapturing, makes it possible to prevent the influence of a flicker peaktiming shift caused by the time difference between the flicker detectionoperation and main image capturing, thus achieving stable flickerlessimage capturing.

FIG. 18C illustrates various control timings related to the flickerdetection operation, the aperture drive, and the light emissionoperations by the light emitting devices when the multi-light emissionmode is enabled (ON) and face detection is currently being performed(YES in step S605).

In a situation as illustrated in FIG. 18C, the CPU 104 performspre-light emission by each light emission group of a plurality of lightemitting devices (slave stroboscopes EGr to BGr) performing multi-lightemission, and acquires the integration result. At this timing, the CPU104 does not perform pre-light emission by the external stroboscope 300serving as the master stroboscope, and therefore has not yet completedthe calculation of the main light emission amount.

Then, the CPU 104 changes the drive control of the image sensor 101 tothe drive control for flicker detection and performs the flickerdetection operation. Then, immediately before image capturing, the CPU104 performs pre-light emission by the master stroboscope (externalstroboscope 300) and calculates the main light emission amount based onthe integration result and other integration results of pre-lightemission previously performed by the light emitting devices serving asthe other light emission groups (light amount control calculation). Uponcompletion of the flicker detection operation, the CPU 104 changes theaperture value from the aperture value for live view display (flickerdetection) to the aperture value for main image capturing.

In this configuration, when a person is detected, the light emittingdevice serving as the master stroboscope performs pre-light emissionimmediately before main image capturing, and front light emission towardthe person is performed immediately before main image capturing. Thismakes it possible to perform image capturing while preventing person'seye shutting. In addition, since the flicker detection operation isperformed immediately before pre-light emission by the light emittingdevice serving as the master stroboscope, it is possible to prevent theinfluence of a flicker peak timing shift caused by the time lapse sincethe flicker detection, thus achieving stable flickerless imagecapturing.

Although, in the present embodiment, the timing of pre-light emissionrelated to the light amount control calculation is controlled by usingas the master stroboscope the light emission group including theexternal stroboscope 300 directly attached to the camera main body 100,the present invention is not limited thereto. For example, whenperforming multi-light emission, the user may specify the masterstroboscope Gr. In this case, the light emission group including thelight emitting device located in front of a person may be used as themaster stroboscope (Gr).

The following describes each operation according to the difference inthe shutter driving method and the presence or absence of detection of amoving object in a case where flickerless image capturing accompanied bylight emission is performed during live view display, with reference toFIG. 19. FIG. 19 is a flowchart illustrating flicker detectionprocessing in light emission image capturing in consideration of thedifference in the shutter driving method and the result of the movingobject detection according to the fourth embodiment of the presentinvention. Processing in step S701 illustrated in FIG. 19 is identicalto the processing in step S601, and processing in steps S706 to S713 isidentical to the processing in steps S605 to S612, respectively, andredundant descriptions thereof will be omitted.

When the multi-light emission setting is disabled (OFF) (NO in stepS701), the processing proceeds to step S702. In step S702, the CPU 104determines whether the shutter driving method in main image capturing isa method using a mechanical front curtain (mechanical front curtainmethod). According to the present embodiment, the shutter driving methodin the charge accumulation period control on the image sensor 101 isclassified into two methods. One method is what is called a mechanicalfront curtain method in which the travel timing of a first blade group(front curtain) and a second blade group (rear curtain), mechanicalshading blades included in the shutter 102, is controlled to adjust thecharge accumulation period of the image sensor 101 by using both thefront and the rear curtains. The other method is what is called anelectronic front curtain method in which the reset timings of the secondblade group (rear curtain) included in the shutter 102 and the imagesensor 101 are controlled to implement the operation equivalent to thefunction of the above-described front curtain through chargeaccumulation control on the image sensor 101. According to the presentembodiment, the execution timing of each operation is differentiatedaccording to the shutter driving method to prevent the increase in thetime difference between the flicker detection operation and main imagecapturing, resulting from the increase in the release time lag occurringwhen the mechanical front curtain method is adopted.

If the shutter driving method is not the mechanical front curtain method(i.e., the shutter driving method is the electronic front curtainmethod) (NO in step S702), the processing proceeds to step S703.Processing in steps S703 to S705 is almost identical to the processingin steps S602 to S604, respectively, and redundant descriptions thereofwill be omitted. On the other hand, when the shutter driving method isthe mechanical front curtain method (YES in step S702), the processingproceeds to step S714. In step S714, the CPU 104 determines whether theamount of movement of the image pickup target subject is a predeterminedamount or larger (i.e., the subject is a moving object). The movingobject detection is performed by the CPU 104 based on a plurality ofimages captured in advance (or captured at this timing) by the imagesensor 101. More specifically, the CPU 104 calculates a motion vector inthe plurality of the images and, if the amount of movement of thesubject based on the motion vector is a predetermined threshold value orlarger, the CPU 104 detects that the subject is a moving object.

When a moving object is not detected (NO in step S714), the processingproceeds to step S715. In steps S715 to S717, the CPU 104 performsoperations in order of pre-light emission by the external stroboscope300 (and the light amount control calculation), the flicker detectionoperation, and the image capturing aperture control. Details of eachoperation are as described above, and redundant descriptions thereofwill be omitted.

On the other hand, when a moving object is detected (YES in step S714),the processing proceeds to step S718. In steps S718 to S720, the CPU 104performs operations in order of the flicker detection operation, theimage capturing aperture control, and pre-light emission by the externalstroboscope 300 (and the light amount control calculation). Details ofeach operation are as described above, and redundant descriptionsthereof will be omitted.

By adopting the above-described configuration, the camera main body 100according to the present embodiment can prevent the influence of therelease time lag accompanying the operation of the shutter 102 on theflicker detection operation. When the subject is a moving object, thecamera main body 100 according to the present embodiment performspre-light emission immediately before main image capturing to minimizethe time difference between pre-light emission and main image capturingaccompanied by main light emission, thus reducing an image pickupfailure resulting from the motion of the subject.

The present embodiment has been described above centering on control inlight emission image capturing using the external stroboscope 300 or asimilar external light emitting device. The above-describedconfiguration is also applicable to light emission image capturing usingthe built-in stroboscope 114.

First Modification

The following describes a first modification of the above-describedsecond embodiment, with reference to FIG. 20. FIG. 20 is a flowchartillustrating flickerless image capturing processing in a case where theflickerless image capturing function is ON, according to the firstmodification of the present invention. Processing illustrated in FIG. 20differs from the processing illustrated in FIG. 10 in that processing insteps S406 and S413 is deleted, processing in step S801 is performedinstead of step S409, and processing in step S802 is performed insteadof step S412. Of the processing illustrated in FIG. 20, processingidentical to the processing illustrated in FIG. 10 is assigned the samereference numerals as the processing illustrated in FIG. 10, andredundant descriptions thereof will be omitted.

According to the present modification illustrated in FIG. 20, in stepS801 (like step S401), the CPU 104 calculates the photometry value BvAvebased on the image for live view display.

In step S802 (like step S405), the CPU 104 calculates the exposureconditions (Tv, Av, and ISO sensitivity) for main image capturing basedon the photometry value BvAve acquired in step S801.

As described above, according to the present modification, in the secondand subsequent image pickups in continuous image capturing, the CPU 104acquires the photometry value to be used when calculating the imagecapturing parameters (exposure conditions) for main image capturing,based on the image for live view display. In this case, as in the caseof performing photometry by using a recording image (still image)captured in main image capturing, there is no possibility that theexposure correction amount is calculated in a duplicated way. Therefore,it is not necessary to calculate the exposure correction amount in thecurrent image pickup by using the exposure correction amount used in thelast image pickup. Therefore, if the configuration according to thepresent modification is adopted, it is possible, when performingflickerless image capturing during live view display, to effectivelyprevent the image brightness from becoming unnatural while restrictingthe increase in the processing load.

Second Modification

The following describes a second modification of the above-describedsecond embodiment, with reference to FIG. 21. FIG. 21 is a flowchartillustrating the flickerless image capturing processing in a case wherethe flickerless image capturing function is ON, according to the secondmodification of the present invention. Processing illustrated in FIG. 21differs from the processing illustrated in FIG. 10 in that theprocessing in steps S901 and S902 is added. Of the processingillustrated in FIG. 21, processing identical to the processingillustrated in FIG. 10 is assigned the same reference numerals as theprocessing illustrated in FIG. 10, and redundant descriptions thereofwill be omitted.

Like the second embodiment, the present modification adopts aconfiguration in which the value of the exposure correction amountComp(x) changes according to the exposure time (shutter speed) Tv. In animage capturing mode in which Tv can be fixed (given priority), forexample, in the shutter speed (Tv) priority mode, the quality of acaptured image is not largely affected even if the exposure correctionamount in each main image capturing in continuous image capturingremains unchanged for each of continuous image pickups. According to thepresent modification, therefore, the method for calculating the exposureconditions is differentiated according to whether an image capturingcondition (for example, Tv priority mode) with fixed Tv, out of theexposure control values, (Tv priority) is set.

According to the present modification illustrated in FIG. 21, in stepS901, the CPU 104 determines whether the current image capturingcondition allows Tv to be preferentially set. More specifically,according to the present embodiment, the CPU 104 determines whether thecurrent image capturing mode allows Tv to be set to a fixed valueaccording to the user's manual setting.

When the CPU 104 determines that the current image capturing conditiondoes not allow Tv to be preferentially set (NO in step S901), theprocessing proceeds to step S412. In step S412, the CPU 104 calculatesthe exposure conditions for main image capturing. On the other hand,when the CPU 104 determines that the current image capturing conditionallows Tv to be preferentially set (YES in step S901), the processingproceeds to step S902. In step S902, assuming that the necessity forremoving the influence of the exposure correction amount LastComp in thelast main image capturing is low in the following main image capturing,the CPU 104 sets the photometry value By to Bv1 and calculates theexposure conditions for main image capturing based on the photometryvalue.

As described above, according to the present modification, when an imagecapturing condition in which Tv, out of the exposure conditions for mainimage capturing, is given priority is set, the CPU 104 calculates theexposure conditions for the following main image capturing withouttaking into consideration the exposure correction amount in the lastmain image capturing, in the second and subsequent image pickups incontinuous image capturing. In this case, since Tv is preferentiallydetermined, the influence on the image quality is small between imagescaptured in continuous image capturing. Therefore, if the configurationaccording to the present modification is adopted, the CPU 104 calculatesthe exposure conditions for the current main image capturing (imagecapturing parameters) regardless of the exposure correction amount inthe last main image capturing depending on the image capturingcondition, thus reducing the processing load.

Third Modification

The following describes a third modification of the above-describedsecond embodiment, with reference to FIG. 22. FIG. 22 is a flowchartillustrating the flickerless image capturing processing in a case wherethe flickerless image capturing function is ON, according to the thirdmodification of the present invention. Processing illustrated in FIG. 22differs from the processing illustrated in FIG. 10 in that theprocessing in step S411 is deleted, and the processing in steps S1001,S1002, S1003, and S1004 is performed instead of steps S406, S410, S412,and S413, respectively. Processing identical to the processingillustrated in FIG. 10, out of processing illustrated in FIG. 22, isassigned the same reference numerals as the processing illustrated inFIG. 10, and redundant descriptions thereof will be omitted.

As illustrated in FIG. 22, in step S1001, the CPU 104 stores the shutterspeed (exposure time) Tv(x), out of the exposure conditions calculatedin step S405, under an alias LastTv in a predetermined area of therecording unit 112.

In step S1002, the CPU 104 performs the flicker detection operation byusing the same method as step S403. In step S1002, there is no branchprocessing corresponding to the flicker detection result. Morespecifically, according to the present modification, in step S1002, theCPU 104 does not calculate the exposure correction amount regardless ofthe presence or absence of a flicker.

In step S1003, the CPU 104 sets the photometry value By to Bv1 andcalculates the exposure conditions for main image capturing based on thephotometry value. However, the CPU 104 sets the shutter speed Tv, out ofthe exposure conditions calculated in step S1003, as LastTv whichcorresponds to the shutter speed calculated for the last main imagecapturing. In step S1004, the CPU 104 stores the shutter speed Tv setfor the current main image capturing under an alias LastTv in apredetermined area of the recording unit 112.

As described above, according to the present modification, in the secondand subsequent image pickups in continuous image capturing, the CPU 104calculates the exposure conditions for the following main imagecapturing by fixing the shutter speed Tv set first. In this case, sincethe shutter speed remains unchanged, the CPU 104 calculates the exposureconditions for the current main image capturing (image capturingparameters) regardless of the exposure correction amount in the lastmain image capturing, in the second and subsequent image capturing incontinuous image capturing, thus reducing the processing load.

While the present invention has specifically been described based on theabove-described embodiments and modifications, the present invention isnot limited thereto but can be modified in diverse ways within the ambitof the appended claims. For example, although, in the above-describedembodiments and modifications, the shutter speed, aperture value, andISO sensitivity are used as the exposure conditions, exposure controlvalues related to other elements may be added to the exposureconditions. For example, if the camera main body 100 or the imaging lens200 includes a light attenuation unit for attenuating the amount oflight incident to the image sensor 101, such as a normal density (ND)filter, the image pickup apparatus 100 may be configured to perform theexposure control in consideration of an exposure control value relatedto the density of the ND filter.

Although, in the above-described embodiments and modifications, thecomponents of the image pickup system centering on the camera main body100, such as the CPU 104 and the recording unit 112, operate in acollaborative way to control the overall operations of the image pickupapparatus 100, the present invention is not limited thereto. Forexample, a (computer) program according to each of the above-describedflowcharts illustrated in FIGS. 3, 8, 9, 10, 14, 17, and 19 to 22 isprestored in a predetermined area of the recording unit 112. The CPU 104executes the program to control the operations of the entire imagepickup system. The program may be formed as an object code, a programexecuted by an interpreter, or script data supplied to an operatingsystem (OS) as long as the program provides programmed functions. Arecording medium for supplying the program may be, for example, a harddisk, a magnetic recording medium such as a magnetic tape, or anoptical/magnetooptical recording medium.

In the above-described embodiments, an image pickup apparatus composedof the camera main body 100 as an image pickup apparatus main body andthe imaging lens 200 separately formed, what is called alens-interchangeable type image pickup apparatus, is used as an exampleof an image pickup apparatus according to the present invention.However, the present invention is not limited thereto. For example, animage pickup apparatus composed of a camera main body and an imaginglens integrally formed, what is called a lens-integrated type imagepickup apparatus, may be used as an image pickup apparatus according tothe present invention.

Although, in the above-described embodiments, a digital camera is usedas an example of an image pickup apparatus according to the presentinvention, the present invention is not limited thereto. For example,the present invention is also applicable to a configuration applying animage pickup apparatus other than a digital camera, such as a portabledevice (a digital camera or a smart phone), a wearable terminal, or asecurity camera.

Other Embodiments

The present invention can also be achieved when a program forimplementing at least one of the functions according to theabove-described embodiments is supplied to a system or apparatus via anetwork or storage medium, and at least one processor in a computer ofthe system or apparatus reads and executes the program. In addition, thepresent invention can also be achieved by a circuit (for example, anapplication specific integrated circuit (ASIC)) for implementing atleast one function.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toembodiments, it is to be understood that the invention is not limited tothe disclosed embodiments. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

What is claimed is:
 1. An image pickup apparatus including an imagesensor and configured to display a live view of images on a displayunit, the image pickup apparatus comprising: a first operation memberoperable manually by a user to give an image pickup preparationinstruction or an image pickup instruction; a second operation memberoperable manually by the user to instruct to start a flicker detectionoperation; and at least one processor or circuit configured to performthe operations of the following units: detection unit configured toperform the flicker detection operation to detect a flicker based on animage captured by the image sensor; and control unit configured tocontrol the image sensor based on flicker information detected by thedetection unit, wherein the detection unit is configured to performfirst detection of the flicker detection operation at a time that isdifferent from a time at which the image pickup preparation instructionis received and different from a time at which the image pickupinstruction is received in a case that the user performs an operation onthe second operation member whilst live view images are displayed on thedisplay unit, wherein the detection unit is configured to perform seconddetection of the flicker detection operation in a case that the userperforms an operation on the second operation member whilst live viewimages are displayed on the display unit, and wherein, in the case thata flicker is detected in the first detection, the control unit isconfigured to control driving of the image sensor so that exposure forobtaining an image for live view display on the display unit after thefirst detection is performed in a charge accumulation period to reducean influence of the flicker.
 2. The image pickup apparatus according toclaim 1, wherein, in the case that a flicker is detected in the seconddetection, the control unit is configured to control the image sensorfor capturing a still image so as to reduce an influence of flicker inaccordance with the operation by the first operation member.
 3. Theimage pickup apparatus according to claim 1, wherein the detection unitis configured to perform the first and the second detections in the casethat a first setting for performing an image pickup in accordance with apredetermined timing of a light amount change of the flicker is presetto ON, and the detection unit is configured to perform the firstdetection without performing the second detection in the case that thefirst setting is preset to OFF.
 4. The image pickup apparatus accordingto claim 1, wherein the detection unit is configured to perform thirddetection of the flicker detection operation before live view display isstarted, and wherein, in the case that a flicker is detected in thethird detection, the control unit is configured to control the imagesensor to achieve an charge accumulation period for reducing aninfluence of the flicker for live view display on the display unit afterthe third detection.
 5. The image pickup apparatus according to claim 1,further comprising: notification unit configured to notify the user thata flicker has been detected in the case that a flicker is detected inthe flicker detection operation, wherein the notification unit notifiesthe user that a flicker has been detected in the case that a flicker isdetected in the first detection.
 6. The image pickup apparatus accordingto claim 5, wherein the notification unit notifies the user that aflicker has been detected by displaying a predetermined icon on thedisplay unit during live view display.
 7. The image pickup apparatusaccording to claim 6, wherein the detection unit is configured toperform the first detection without updating the live view displaying.8. The image pickup apparatus according to claim 1, wherein thedetection unit is configured to perform the flicker detection operationbased on a plurality of images that are captured at intervals which areshorter than intervals at which images for live view display arecaptured.
 9. A method for controlling an image pickup apparatusincluding an image sensor and a first operation member operable manuallyby a user to give an image pickup preparation instruction or an imagepickup instruction and a second operation member operable manually bythe user to instruct to start a flicker detection operation andconfigured to display a live view of images on a display unit, thecontrol method comprising: detecting a flicker by performing the flickerdetection operation to detect a flicker based on an image captured bythe image sensor; and controlling the image sensor based on detectedflicker information, wherein, in the detection, first detection of theflicker detection operation is performed at a time that is differentfrom a time at which the image pickup preparation instruction isreceived and different from a time at which the image pickup instructionis received in a case that the user performs an operation on the secondmember whilst live view images are displayed on the display unit,wherein, in the detection, second detection of the flicker detectionoperation is performed in a case that the user performs an operation onthe second operation member whilst live view images are displayed on thedisplay unit, and wherein, in the case that a flicker is detected in thefirst detection, driving of the image sensor is controlled so thatexposure for obtaining an image for live view display on the displayunit after the first detection is performed in a charge accumulationperiod to reduce an influence of the flicker.
 10. A non-transitorycomputer-readable storage medium corresponding to instructions which,when executed by a processor, cause the processor to carry out themethod of claim 9.